An internal combustion engine is provided with a number of cylinders, each of which is connected to an intake manifold by means of at least one intake valve and to an exhaust manifold by means of at least one exhaust valve. The intake manifold receives fresh air (i.e. air from the external environment) through a feeding pipe adjusted by a butterfly valve and is connected to the cylinders by means of corresponding intake pipes, each of which is adjusted by at least one intake valve.
The introduction of a swirl system, which is adapted to vary the section of the intake pipes during the engine operation according to the speed of the engine itself (i.e. to the angular rotation speed of the drive shaft), has recently been suggested. At low speeds, the air introduction section through the intake pipes is decreased so as to generate turbulences in the aspirated air flow which improve the air and fuel mixing in the cylinders; in virtue of the presence of these turbulences which improve mixing, all the injected fuel is burnt and thus the polluting emissions generated by the combustion are reduced. At high speeds, the air introduction section through the intake pipes is maximized so as to allow a complete filling of the cylinders, and thus to allow the generation of the maximum possible power.
In order to vary the air introduction section through the intake pipes, each intake pipe has two reciprocally parallel channels, only one of which may be completely closed by a butterfly choking valve. At low speeds, the butterfly choking valves are closed, therefore reducing the air introduction section through the intake pipes, while at high speeds the butterfly choking valves are opened to maximize the air introduction section through the intake pipes.
In the currently marketed engines, it has been suggested to use a single common actuator device, which simultaneously and synchronically actuates all the choking valves; specifically, the actuator device comprises a stiff bar, which is mechanically connected to all the choking valves so as to simultaneously and synchronically actuate all the choking valve themselves, and an electric motor, which is mechanically connected to the bar to control the displacement of the bar between two limit positions corresponding to the closing and maximum opening positions of the choking valves. The two limit positions of the bar corresponding to the closing and maximum opening positions of the choking valves and are defined by two mechanical stroke ends which are mechanically coupled to the electric motor. The actuator device further comprises a position sensor, which is coupled to the electric motor and indirectly detects the position of the bar to allow a feedback control of the electric motor itself; furthermore, the position sensor is also used to check the actual operation of the actuator device and thus indicate a possible malfunctioning of the actuator device itself according to the indications of OBD2 (On Board Diagnose 2) standards. Indeed, a malfunctioning of the actuator device compromises the correct operation of the swirl system, and may thus determine an increase of polluting emissions generated by combustion, particularly at low speeds.
However, according to the specifications defined by the United States CARB (California Air Resources Board), checking the operation of the above-described swirl system is not sufficient, because it allows to only check that the electric motor is operating on the bar but does not check if the bar is correctly transmitting motion to all the choking valves; in other words, the check of the operation of the above-described swirl system is not able to diagnose the breakdown of the mechanical connection between a single choking valve and the bar. Therefore, the above-described swirl system does not meet the approval requirements established by CARB and thus may not be approved in the United States.
In order to comply with the approval requirements established by CARB, it has been suggested to couple a position sensor to each choking valve; however, this solution is expensive both for the cost related to the position sensors and for the cost related to the mechanical assembly and to the wiring of the position sensor themselves.